Lobbying is just people or organizations making their case to politicians in a private way (e.g. meeting MP in their office) instead of a public way (e.g. putting an article to press).
Somehow it seems different when 'presenting the case' is accompanied by gifts and money.
This is the main problem, and there is a solution. If campaigns are financed by enough public money, donations have less power and can be regulated more heavily.
Similarly, if individual politicians get enough from the state to feel secure even if voted out, we take away the power of the promise of a next job and can enforce a grace period before working on anything related.